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A coalition of civil liberties groups has asked a federal appeals court to revisit a recent ruling that held the police did not violate the Fourth Amendment when they tracked suspect Melvin Skinner's cell phone without a warrant. A Tuesday brief argues that a three-judge panel of the Sixth Circuit Court of Appeals had misunderstood both the relevant Supreme Court precedents and the technical details of how the police had accomplished the tracking. The groups—the American Civil Liberties Union, the Electronic Frontier Foundation, and the Center for Democracy and Technology—want the case re-heard by a panel of all Sixth Circuit judges.

The legal arguments in the case center on US v. Jones, a Supreme Court decision from earlier this year that found it unconstitutional to attach a GPS device to a car and track it for 28 days without a warrant. In contrast, the police tracked Skinner using the GPS in his cell phone instead of attaching a separate GPS device to his car. And they tracked him for only 3 days rather than 28.

The Sixth Circuit majority ruled that the police had simply picked up GPS signals that had been "emitted" by Skinner's phone and used it to track his movements. But the civil liberties groups point out that this is an over-simplified description of how the signals were obtained. Cell phones do not routinely emit location data derived from GPS measurements; they do so only when their phone companies remotely activate a phone's tracking capabilities. This fact, the civil liberties groups argue, should subject the tracking to a higher level of scrutiny.

The groups also argued the tracking violated the Fourth Amendment despite its relatively short duration. The courts have ruled that long-term tracking is more likely to trigger Fourth Amendment scrutiny than temporary tracking. While the 3-day tracking of Skinner was much shorter than the 28 days of tracking in the Jones case, the ACLU brief argues that tracking a cell phone is much more invasive than tracking a car. A car spends most of its time sitting in a driveway or parking lot. In contrast, many people carry their cell phones in their pockets or purses everywhere they go. Hence, the groups argue, 3 days of cell-phone tracking could provide more personal information about a suspect than 28 days of car location data.

"The panel majority opinion is an unusually important and weighty precedent given its status as the first appellate decision in the nation to apply Jones to GPS tracking via cell phones," the brief states. It argues that the original decision was made in haste and failed to take into account all the complexities of the issue.